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Abstract

To obtain a phase distribution without the use of an optical path besides an object beam, a reference-free holographic diversity interferometry (RF-HDI) has been proposed. Although the RF-HDI can generate an internal reference beam from the object beam, the method has a problem of measurement accuracy due to insufficient power of the internal reference beam. To solve the problem, we newly propose a RF-HDI via iterative measurements. Our method improves the measurement accuracy by utilizing iterative measurements and feedback of each obtained phase image to the measurement system. In the experiment, the phase image, which has a random pattern, can be measured as an object beam with a higher accuracy than in the conventional RF-HDI. To support this result, we also evaluated the wavefront accuracy and optical power efficiency of an internal reference beam in this method. As a result, we verified that our method enables us to generate an internal reference beam that has the wavefront of a near single plane wave and a higher power efficiency than the conventional RF-HDI. In addition, our method can be applied to measurement for the modal content in an optical fiber, atmosphere turbulence, etc., where it is difficult to prepare an external reference beam with a high coherency.

Figures (7)

Fig. 1 Schematic diagram of our method; PSLM: phase-type spatial light modulator, and HDI: holographic diversity interferometry, which is a phase-shifting digital holography technique developed in our laboratory. A beam to be measured is divided into two optical paths using a beam splitter; one is used for the object beam, and the other is used for the internal reference beam. In the path of the internal reference beam, a component of a single plane wave (DC-component) is extracted using a spatial filter and a PSLM. Then, by iterative measurements and feedback of each measured image to the internal reference beam through the PSLM, our method obtains a phase image with a high power efficiency and high measurement accuracy without an additional optical path for the reference beam.